Extracting multiple points from matrix and plotting

Hi.

I have a 900 row by 3 column matrix, each corresponding to a centroid of 3 objects. The 3 objects are red, green and blue.

The first column corresponds to the X coordinate, the second corresponds to Y coordinate of the objects centroid, and the 3rd column corresponds to the centroid's colour (1 = red, 2 = green, 3 = blue).

How can I efficiently loop through the matrix and filter all the rows where colour = 1, and plot all the coordinates from top to bottom, and same for the other two? I know this should be easily possible using find, but my matlab isn't great so any help is much appreciated.

Answer 1

[Star Strider]

I would use the sortrows function. It should be able to do what you want.

[Star Strider]

The best way to do that is with a cell array, to avoid creating dynamic variables (a poor programming practise). Here, ‘Mtx{1}’ has all the rows where the third column is 1, and so for the others. The rows remain the same.

The code:

M = [randi(99, 15, 2)  randi(3, 15, 1)];                    % Create Data

for k1 = 1:3
    Mtx{k1} = M(M(:,3) == k1,:);                            % Create Cell Array
end